1. Field of the Invention
The present invention relates in general to split ring castings for retaining boiler tubes in a predetermined spaced configuration, and more particularly to retaining heat shields for same.
2. Description of the Related Art
Steam boilers used for heat generation utilize boiler tubes which are generally exposed and vertically hang downward from a top structure of the boiler and swing free in this position. These tubes are referred to in the industry as secondary super heater or reheat tubes, or heat recovery tubes for recovering lost heat. The boiler structure requires the boiler tubes to be aligned with respect to each other and held in a parallel position.
Known procedures for retaining these boiler tubes together in spaced parallel configuration utilize a split ring casting which is formed from two elongated parallel clamp halves forming a series of circular elements for clamping a series of these tubes in parallel between each circular element such that the tubes are then running perpendicular to the clamped halves.
These clamp halves each have a series of internal semicircular openings which oppose each other when the two bar clamps are aligned in parallel to thereby in combination provide a series of split ring openings in each circular element when the bar clamps are clamped together to form the circular elements and to receive the tubes in parallel alignment in the internal semi-circular areas.
Alignment protrusions usually extend from each of the bar clamp halves toward the other between each semi circular recess. Opposing alignment openings are provided between each recess on the other clamp half to receive the respective alignment protrusions therethrough so that when the bars are clamped together in parallel engagement the protrusions extending from each bar half are guided through the opposed alignment openings in the other bar half so that when the clamp halves are fully engaged they form a series of rings for aligning and retaining the tubes therein in a parallel series.
The clamp halves of the split ring casting are clamped together, and the parallel clamp halves are then welded together to retain the tubes in their parallel alignment. Thereafter the clamp, if employed, on the bar clamps can be removed.
The described split ring castings work well in retaining the boiler tubes in proper relationship, but they have one difficulty. On boiler units having high gas temperatures, or in locations with high gas temperatures, the front portion of the split ring castings overheat and oxidize and the weld that joins the split ring castings together (located on the end of the split ring casting) fails. This oxidation and weld failure leads to the failure of the casting. Failure of the casting cause misalignment of the boiler tubes. Replacement of the split ring casting is expensive and very time consuming since the old casting must be removed, then the tubes realigned in the new casting, and the halves of the casting then clamped in place. The new casting is then welded together and the clamps removed if clamps are employed. Through bolt split ring castings can eliminate the requirement of the clamps.
Thus a split ring casting design is needed which does not suffer from failed weld joints when subjected to a high temperature environment or heat front.